The present invention relates to a friction bonding method and apparatus and a holding tool used for the friction bonding apparatus, and relates to a friction bonding method and apparatus and a holding tool used for the friction bonding apparatus suitable for manufacturing an electronic circuit board and a suspension head by mounting an electronic component on a base member such as a semiconductor element on, for example, a circuit board or a magnetic reading suspension head with metallic bonding when metallically bonding the objects to be bonded to each other.
For example, with an increasing number of functions of electronic equipment and an increasing number of electronic components, electronic circuit boards tend to receive miniaturized electronic components at increasing mounting densities, and the flip chip mounting technology for mounting electronic components by providing metallic bumps on electrodes formed on a semiconductor wafer and metallically bonding the metallic bumps with a wiring pattern formed on a circuit board is also used for manufacturing an electronic circuit board. This can easily cope with the miniaturization, the fine structure, and the increase in mounting densities of electronic components and connection routes.
The metallic bonding is achieved typically by friction bonding utilizing ultrasonic vibrations. Of course, being not limited to this, the metallic bonding can also be achieved generally by frictional contact with a relative movement.
However, a comparatively strong frictional contact by pressurization and vibratory relative movement is needed for the metallic bonding by frictional contact between minute metallic bonding portions. However, as the semiconductor element becomes more minute, the metallic bumps formed on the element become very small, and the electrodes and wiring portions of the circuit pattern to be metallically bonded to this also become thin. Therefore, the frictional contact is prone to be excessive, possibly damaging the metallic bumps and the circuit pattern, causing a short-circuit as a consequence of the excessive collapse of the metallic bumps striding over the fine circuit pattern and causing defective sealing as a consequence the failure in the entry of the sealant of an excessively reduced gap between the circuit board and the semiconductor element due to the excessive collapse of the metallic bumps. If the frictional contact is reduced in order to avoid the above troubles, then the metallic bonding becomes insufficient, and the semiconductor element, which has been estimated to be bonded, subsequently falls off to make the electronic circuit board defective or causes a failure at an early stage.
Lately, there has been known the technology of using a suspension head 400b constructed of a thin leaf spring for reading a magnetic disk 400a as shown in FIG. 15. The suspension head 400b is supported so that its base portion can be pivoted by a rotary shaft 400c, and read is executed by scanning the magnetic disk 400a with a reading portion 400d located at its tip portion in an arc in the radial direction and rotating the magnetic disk 400a around a spindle 400e. A number of sensing terminals are arranged in the read portion 400d of the suspension head 400b, and a semiconductor element 400f for read is bonded onto wiring lines extended from the sensing terminals to the base portion side of the suspension head 400b. 
The semiconductor element 400f is bonded to the base portion side of the suspension head 400b where the width is comparatively large and the wiring interval is increased, and connected to the wiring pattern by way of a bonded wire 400g. 
However, with increasing in the read speed, the semiconductor element 400f for read use are demanded to be bonded to a portion in the vicinity of the read portion 400d located at the tip portion of the suspension head 400b. However, since the tip portion of the suspension head 400b is thin and has very small intervals of wiring, it is difficult to perform bonding by wire connection according to the wire bonding method. If it is attempted to cope with this by replacement with the metallic bonding of the semiconductor element 400f provided with metallic bumps, then the semiconductor element 400f is required to have a very small size of not larger than 2-mm square according to circumstances, and a positional accuracy of not greater than 0.3xcexc is needed for the bonding. Moreover, if foreign materials (particles) adhere to the read portion and the wiring lines of the suspension head 400b as a consequence of the occurrence of silicon powder from the semiconductor element 400f when ultrasonic vibrations are applied to the semiconductor element 400f during friction bonding via a suction tool that sucks and holds the element 400f or for another reason, then the read characteristics of the element are often impaired, reducing the yield.
Such foreign materials are generated not only in the case of a silicon semiconductor element but also in the case of a GaSi semiconductor element. Moreover, the same thing can be said for LiTa, LiNb, and the like used for a SAW (Surface Acoustic Wave) element, and it is also generated in the case of crystal. The foreign materials generated from these materials mean the scrapes, scratches, and chipping of the back surface of the semiconductor element 400f itself, which leads to the roughness and smear of the back surface, solely causing a reduction in quality after bonding. Furthermore, with an increase in the frequency of repetition of bonding by the suction tool, those foreign. materials adhere to the suction surface of the suction tool and gradually accumulate. This also causes the further roughness of the back surface of the semiconductor element 400f to be bonded, worsening the quality of the semiconductor element 400f, and further reducing the yield because of easy occurrence of chipping and cracking of the element inclusive of the electrodes.
In order to cope with this, it is attempted to reduce the ultrasonic output from the normal value of 1 W to 0.1 W or reduce the friction bonding time by ultrasonic waves from the normal value of 0.5 sec to 0.1 sec. However, this attempt tends to cause defective bonding. It is also attempted to clean the suction surface of the suction tool by periodic polishing, the required extra work degrades the productivity, and there is another issue that the operating life of the suction tool is shortened by the abrasion due to polishing.
When bonding the semiconductor elements 400f to the suspension head 400b, a number of suspension heads 400b are arranged parallel so as to integrally extend from a frame portion to the inside of the frame portion, allowing the whole body to be handled as one plate-shaped member. Therefore, the heads can be handled similarly to the circuit board to which electronic components are bonded.
However, each suspension head 400b has its base portion connected to the frame portion by two narrow connecting portions. According to the experiments carried out by the present inventors, the head is thin and easily deformed, and if the head is deformed even a little bit, it is difficult to correct the deformation, leading to a defective product and reduced yield. In particular, it has been difficult to reliably bond the semiconductor element 400f to the suspension head 400b by the friction bonding performed conventionally without the troubles of damage and so on.
The present inventors, who repetitively carried out various experiments and examinations in order to solve this issue, discovered that the proper method was to temporarily reduce or stop the friction bonding operation for metallic bonding partway.
The object of the present invention is to provide a friction bonding method and apparatus capable of performing metallic bonding just enough without damage on the objects to be bonded to each other and a holding tool used for the friction bonding apparatus, on the basis of the aforementioned newly obtained knowledge.
In order to achieve the aforementioned object, the present invention is constructed as follows.
According to a first aspect of the present invention, there is provided a friction bonding method comprising: temporarily reducing or stopping a friction bonding operation partway when a semiconductor element and a circuit forming body, which are two objects to be bonded to each other, are pressurized against each other and relativity moved to put a plurality of metal electrode portions of the semiconductor element and a plurality of metal electrode portions of the circuit forming body, as metallic bonding portions, into frictional contact with each other so as to perform friction bonding of the metallic bonding portions.
According to a second aspect of the present invention, there is provided a friction bonding method according to the first aspect, wherein the friction bonding operation is temporarily reduced or stopped partway when the metallic bonding portions are frictionally bonded to each other by the frictional contact between the metallic bonding portions by pressurizing and relatively moving the semiconductor element that is one object to be bonded of the two objects to be bonded relative to the circuit forming body that is the other object to be bonded of the two objects to be bonded in a state in which the one object to be bonded is held by a holding tool with the metallic bonding portions of the objects to be bonded facing each other.
According to a third aspect of the present invention, there is provided a friction bonding method according to the second aspect, wherein the holding tool is a suction tool, and the friction bonding operation is temporarily reduced or stopped partway when the metallic bonding portions are frictionally bonded to each other with the metallic bonding portions put into frictional contact with each other by sucking and holding the semiconductor element that is the one object to be bonded of the two objects to be bonded by the holding tool with the metallic bonding portions facing each other and pressurizing and relatively moving the one object to be bonded with respect to the circuit forming body that is the other object to be bonded of the two objects to be bonded.
According to a fourth aspect of the present invention, there is provided a friction bonding method according to any one of the first through third aspects, wherein the relative movement is performed by subjecting the semiconductor element that is the one object to be bonded of the two objects to be bonded to ultrasonic vibrations.
According to a sixth aspect of the present invention, there is provided a friction bonding method according to the third aspect, wherein, when sucking and holding the semiconductor element that is the one object to be bonded by the suction tool, the one object to be bonded is sucked and held by being put in contact with and received by a pair of opposed taper surfaces that is formed on a suction surface of a suction nozzle and able to be brought in contact with an external edge portion of the one object to be bonded.
According to a seventh aspect of the present invention, there is provided a friction bonding method according to any one of the first through sixth aspects, wherein the temporary reduction of the friction bonding operation is performed by reducing the relative movement between the metallic bonding portions.
According to an eighth aspect of the present invention, there is provided a friction bonding method according to any one of the first through sixth aspects, wherein the temporary stop of the friction bonding operation is performed by stopping the relative movement between the metallic bonding portions.
According to a ninth aspect of the present invention, there is provided a friction bonding method according to the seventh or eighth aspect, wherein the temporary reduction or stop of the friction bonding operation is performed by stopping the pressurization between the metallic bonding portions.
According to a 10th aspect of the present invention, there is provided a friction bonding method according to the ninth aspect, wherein the stop of the pressurization is performed by separating the holding tool away from the one object to be bonded held by the tool.
According to an 11th aspect of the present invention, there is provided a friction bonding method according to any one of the first through sixth aspects, wherein the reduction of the friction bonding operation is performed by reducing the relative movement of the objects to be bonded to each other and the pressurization between the metallic bonding portions.
According to a 12th aspect of the present invention, there is provided a friction bonding method according to any one of the first through 11th aspects, wherein an initial friction bonding operation before the reduction or stop is performed by controlling a distance between the objects to be bonded to each other, and a final friction bonding operation after the reduction or stop is performed by controlling the pressurization between the objects to be bonded to each other.
According to a 13th aspect of the present invention, there is provided a friction bonding method according to any one of the first through 11th, wherein an initial friction bonding operation before the reduction or stop is performed by controlling the pressurization between the objects to be bonded to each other, and a final friction bonding operation after the reduction or stop is performed by controlling a distance between the objects to be bonded to each other.
According to a 14th aspect of the present invention, there is provided a friction bonding method according to any one of the first through 13th, wherein an initial friction bonding operation before the reduction or stop is performed for a time shorter than a time of a final friction bonding operation after the reduction or stop.
According to a 15th aspect of the present invention, there is provided a friction bonding method according to any one of the first through 13th, wherein an initial friction bonding operation before the reduction or stop is performed by controlling a distance between the objects to be bonded to each other, and on basis of control data obtained at the time, the distance between the objects to be bonded to each other is controlled during a final friction bonding operation after the reduction or stop.
According to a 16th aspect of the present invention, there is provided a friction bonding method according to any one of the first through 15th aspects, wherein an initial friction bonding operation before the reduction or stop is performed by controlling the pressurization between the objects to be bonded to each other, and on basis of control data obtained at the time, the pressurization between the objects to be bonded to each other is controlled during a final friction bonding operation after the reduction or stop.
According to a 17th aspect of the present invention, there is provided a friction bonding method according to the fourth aspect, wherein the friction bonding operation is temporarily reduced or stopped partway when the metallic bonding portions are frictionally bonded to each other through the frictional contact between the metallic bonding portions by pressurizing and moving one object to be bonded of the two objects to be bonded relative to the other object to be bonded of the two objects to be bonded in a state in which the one object to be bonded is held by a holding tool with the metallic bonding portions of the objects to be bonded facing each other, an impedance of a ultrasonic horn connected to an oscillator attached onto the holding tool is monitored during an initial friction bonding operation before the reduction or stop when performing frictional bonding by the ultrasonic vibrations, and a final friction bonding operation after the reduction or stop is controlled in accordance with the monitored impedance.
According to an 18th aspect of the present invention, there is provided a friction bonding method according to the fourth aspect, wherein the one object to be bonded of the two objects to be bonded is a semiconductor element, and the other object to be bonded of the two objects to be bonded is a magnetic disk reading suspension head constructed of a thin leaf spring.
According to a 19th aspect of the present invention, there is provided a friction bonding apparatus comprising:
two bonding object handling units for holding the semiconductor element by means of a suction tool, holding a circuit forming body which are the two objects to be bonded, and positioning the semiconductor element and the circuit forming body so that their metal electrode portions that is a plurality of metallic bonding portions respectively face each other by holding the semiconductor element and the circuit forming body respectively;
a relative movement unit for respectively bringing the plurality of opposed metallic bonding portions of the two objects to be bonded into frictional contact with each other by relatively moving the objects to be bonded held by the two bonding object handling units; and
a control unit, which controls the holding and positioning of the objects to be bonded by the bonding object handling units and the relative movement of the bonding object handling units by the relative movement unit so as to respectively make the plurality of metallic bonding portions of the objects to be bonded held by the bonding object handling units face each other and brings the objects into frictional contact with each other by the relative movement for achievement of respective metallic bonding,
the control unit temporarily reducing or stopping the friction bonding operation partway.
According to a 20th aspect of the present invention, there is provided a friction bonding apparatus according to the 19th aspect, wherein movement of one of the bonding object handling units by the relative movement unit is performed by ultrasonic vibrations.
According to a 21st aspect of the present invention, there is provided a friction bonding apparatus according to the 19th or 20th aspect, wherein one object to be bonded of the two objects to be bonded is handled by one bonding object handling unit of the two bonding object handling units, the one object to be bonded is an object to be bonded that has a frame portion and the metallic bonding portion in an inclined portion that extends from the frame portion into the frame portion and is inclined with respect to the frame portion,
the one bonding object handling unit has a positioning section for positioning and holding the frame portion of the one object to be bonded,
the positioning section can move into a unloading/loading position in which the frame portion of the one object to be bonded is held and guided along its conveyance surface and the one object to be bonded is loaded and unloaded and a bonding position in which the is inclined portion of the one object to be bonded that holds and positions the frame portion is inclined so as to extend along the conveyance surface and the metallic bonding portion located at the inclined portion is subjected to metallic bonding,
the one bonding object handling unit further comprises: a position switching unit for performing switching so that the positioning section is moved into the unloading/loading position and the bonding position; and
a backup section for performing backup so that the inclined portion of the one object to be bonded positioned by the positioning section is supported from below when the positioning section is switched to the bonding position, and
the control unit controls the position switching unit according to the loading, unloading, positioning, and bonding of the one object to be bonded, thereby switching the positioning section between the unloading/loading position and the bonding position.
According to a 22nd aspect of the present invention, there is provided a friction bonding apparatus according to the 21st aspect, wherein the positioning section has a pair of guide rails for conveying and guiding the one object to be bonded, the one object to be bonded is a spring leaf, the inclined portion is formed at a tip portion of the spring leaf extended inside the frame portion, and the positioning section is provided with: a pressurizing member that is supported by one guide rail of the pair of guide rails of the positioning section and able to move between a holding position in which the inclined portion owned by the spring leaf is held between the pressurizing member and the backup section and a holding release position in which the holding is released; and a switching unit that switches the pressurizing member into the holding position and the holding release position between the pressurizing member and the one guide rail, and
the control unit controls the switching unit so as to position the pressurizing member in the holding position every time the one object to be bonded is received and positioned in the positioning section and in the holding release position every time the bonding operation ends.
According to a 23rd aspect of the present invention, there is provided a friction bonding apparatus according to the 22nd aspect, wherein a plurality of spring leaves each of which is the one object to be bonded exist inside the frame portion, the pressurizing member is provided with a pressurizing leaf that can hold each spring leaf between the pressurizing member and the backup section while independently covering the spring leaf, the pressurizing leaf holds or releases the holding of the spring leaf, and each pressurizing leaf is provided with a through hole for exposing the metallic bonding portion of the inclined portion of each spring leaf to subject the metallic bonding portion to friction bonding.
According to a 27th aspect of the present invention, there is provided a frictional bonding apparatus according to the 20th aspect, further comprising two bonding object handling units, one bonding object handling unit operable for performing temporary fixation by an initial frictional bonding operation until the reduction or stop of the frictional bonding, and the other bonding object handling unit operable for performing regular fixation by a final frictional bonding operation of the semiconductor element and the circuit forming body after the bonding operation until the reduction or stop of the frictional bonding.
According to a 28th aspect of the present invention, there is provided a frictional bonding apparatus according to the 27th aspect, wherein the one bonding object handling unit for performing the initial frictional bonding operation has a suction tool that has a suction hole for sucking the semiconductor element, and the other bonding object handling unit has an inclined tool that has an inclined surface capable of holding the semiconductor element.